1. Technical Field
The disclosure relates to a shape measurement apparatus and a shape measurement method for performing non-contact measurement of a shape of a curved surface of a component, the curved surface having a spherical shape.
2. Related Art
Examples of a typical spherical component having a spherically curved surface include an optical lens, and a processing plate for processing the optical lens. Conventionally, as a technique of measuring the shape of the curved surface of such a spherical component, there is a known contact type shape measurement technique of performing measurement by allowing a contact type probe to come in contact with a measuring object.
Moreover in recent years, there is a known non-contact type shape measurement technique (for example, refer to JP 9-178439 A and JP 2002-257511 A) of measuring the shape of a measurement surface by measuring a distance to the measurement surface by a distance measurement instrument using light from a laser displacement meter, or the like. The non-contact type shape measurement technique can be used without causing the probe to come in contact with a measuring object. Therefore, it is possible to perform measurement with high accuracy without damaging the measurement surface, or even when the measuring object surface is a rough surface or a discontinuous surface. Furthermore, the non-contact type measurement technique has an advantage of being able to perform measurement in a shorter time compared with conventional contact type measurement techniques.
In the distance measurement instrument using light, distance measurement accuracy might change depending on an illumination angle of illumination light toward a measuring object, that is, inclination of an optical axis of illumination light with respect to a tangent plane on a measurement point. Specifically, the greater the deviation of the illumination angle of the illumination light with respect to the tangent plane from 90°, the lower the measurement accuracy. In order to address such a situation, JP 9-178439 A discloses computational correction of the measurement error due to inclined illumination. Moreover, JP 2002-257511 A sets various stages and a fixture to a relationship based on a fixed algorithm, thereby reducing the reflection angle of the light reflected from a steep surface on an edge portion of the measuring object.